Such a position indicator is already known from the internal company paper "Motorantriebe MA 7, Betriebsanweisung" [translated: Motor Drive MA 7, Operation Instructions", translator's note], Impressum BA 40/90 de-0391/2000 of the applicant.
Thereby the position indicator is designed as a direct integral component of the controlling gear. There are a switching-phase indicating disk and a position indicating disk, both of which are actuated within the controlling gear. The position display itself is done through the indicia arranged on the frontal, i. e. peripheral side of the respective disk, which turn together with this disk. The frontal sides are visible from the outside in a certain area and the thereon displayed indicia are readable.
The switching-phase indicating disk rotates just like the eccentric disk of the controlling gear, which actuates the individual contacts in a predetermined switching sequence, each time the step switch is switched from one phase or the like to another neighboring phase, each time by a full rotation.
On its frontal side it is provided with indicia which represent, respectively illustrate with digits or other symbols, the individual switching phases, i.e. switching sequence taking place one after the other during a switch.
A green field indicates the rest position of the cam switch.
The starting point of a switching phase, i.e. the stationary state of the motor drive, is represented by a red central mark within the green area.
The position-indicating disk is provided on its frontal side with digits or the like, which correspond to the possible switch position of the respective step switch or the like.
The position indicating disk rotates each time there is a switch from one step of the step switch to a neighboring other step, each time by an angle, i.e. by a phase which corresponds to the distance between two neighboring indicia.
Thus by means of the switching-phase indicator disk, the known position indicator shows each time in which area of the switching sequence the motor drive is located at that time, during a switch.
Further by means of the position-indicating disk it also indicates the operational position wherein the drive motor is located (in the stationary state).
The disadvantage of this known position indicator is the poor visual representation of the switching operation, i.e. of the respective switching sequence to be passed. It is not easy to recognize whether an initiated switching operation is in its initial stage or close to its completion.
A further disadvantage consists in that the displays, which as already explained are located on each of the frontal sides of the two disks can not be read from a greater distance. Since both disks are components of the controlling gear and the frontal discs can not be made as thick as desired, an enlargement of the digits or of other symbols is precluded by the construction conditions.
A further disadvantage of the known position indicator consists in that it can not indicate which operational positions have already been assumed during the preceding actuation of the motor drive, i.e. which control range of the step switch or the like has been used up to the present point in the practical operation, if at all. However such information is of increasing importance for service, setting and monitoring functions. It is important to know for instance whether a step switch was switched through its entire control range or it was operated basically only in a narrowly limited area, and whether this narrowly limited area is in a given case close to one of the end positions. All this information can not be obtained from the known position indicator.